Generally, an automobile wheel of light alloy in the form of an assembly of a wheel disk and a tire supporting wheel rim is known, said wheel disk being interchangeably fitted on the hub of an axle.
It has been common practice to form a number of vent holes in the intermediate region between the boss and the peripheral rib of the wheel disk to distribute them thereover, thereby providing a quasi-wire spoke configuration or other artistic pattern on the surface of the wheel disk.
Such artistically designed pattern has become the selling point for interchangeable wheels, which tend to be manufactured on a diversified small- and medium-quantity production basis.
However, conventional wheel disks used in light alloy wheels for automobiles are of single construction consisting of a single flat disk, as found in Japanese Patent Application Disclosure No. 227501/1984; the artistic patterns formed thereon are lacking in three-dimensional effect and dignity.
That is, in the single construction, in designing said artistic patterns, there is no way but to thicken the disk itself, to bend all or part of the disk or to expose ribs on the surface of the disk. As a result, the resulting artistic design is unavoidably monotonus. Further, in relation to various automobiles having interchangeable wheels mounted thereon, there is a limit to the obtainment of an artistic pattern full of interest and variety, which is expected to be in harmony with the design of the car body.
As for measures to be taken to solve such problems, it wound be contemplated to mount a separate wheel cap on the entire surface of a wheel disk. With such arrangement, however, even if a beautiful artistic pattern can be imparted to the wheel cap, the wheel cap is nothing but an accessory part to the wheel disk, and since it is attached to the wheel disk afterward, it does not add to the strength of the wheel disk itself. Wheel disks are required to have a sufficient strength to support wheel rims.
Thus, I have previously proposed Japanese Patent Application Disclosure No. 185302/1983, wherein the wheel disk is of double construction consisting of a front wall and a rear wall, the opposed walls being integrally cast in spindle form, so that support members for the rear wall can be seen through vent holes distributed over the front wall.
Thus, despite the fact that the wheel disk is made of light alloy, there is an advantage that an artistic pattern depicting a quasi-wire spoke configuration having a three-dimensional dignified effect can be obtained; thus, it serves to solve the above problems to some extent.
However, the wheel disk of said known invention is a one-piece casting of light alloy and in this sense it does not differ much from a wheel disk of a single construction; it cannot be produced by forging or other plastic processing means which are effective for increasing the strength of the wheel disk.
Further, since it is of one-piece construction, once it is produced the artistic pattern of the wheel disk cannot be changed by changing the combination of said front wall and said rear wall; thus, a wheel disk having an artistic pattern full of variety can hardly be manufactured on a diversified small- and medium-quantity production basis.
Not only in Japanese Patent Application Disclosure No. 227501/1984 but also in applicant's Japanese Patent Application Disclosure No. 185302/1983, the boss of the wheel disk is adapted to be attached to the hub of the axle by a plurality of screw clamp devices extending parallel with the wheel rotation axis.
In this respect, it may be said that means for integrally rotatably attaching the boss of a wheel disk to the hub of an axle through a separate adapter plate. However, in this case also, the situation remains unchanged in that the plurality of screw clamping devices for attaching the boss of the wheel disk to the adapter plate still extend parallel with the wheel rotation axis.
Therefore, supposing that the diameter of the wheel disk is constant, the PCD (Pitch Circle Diameter) of the screw clamping devices for attaching the boss to the hub of the axle directly or indirectly through the adapter plate becomes excessively large and correspondingly thereto the boss of the wheel disk has to be given as large a diameter as possible since it needs the strength for attachement.
If so, the intermediate region between the boss and the peripheral rib of the wheel disk is limited in area, with the result that the degree of freedom for providing said artistic pattern in said region is correspondingly limited; thus, the length of quasi-wire spokes forming such artistic pattern is unavoidably decreased.
In the case of the means for attaching the boss of the wheel disk to the hub of the axle directly or indirectly through the adapter plate by screw clamping devices extending parallel with the wheel rotation axis, the horizontal component of an external force imparted from the road to the wheel produces tensile stresses in said screw clamping devices and shearing stresses also in said screw clamping devices; thus, loads acting in all directions cannot be effectively dispersed or absorbed.
As a result, when it is desired to mount wheel on 4WD cars or 4WS cars, it is very difficult to establish a wheel mount state which provides durability and copes with complicated actions required of the wheels for said cars and changes in the direction of external forces on the wheels.